The principal subject of the planned research will be the mechanical and morphogenetic interaction of tissue cells with the major extracellular protein collagen - more specifically, the ability of fibroblastic cells to exert strong shearing "traction" forces on extracellular materials and to rearrange collagen into anatomical patterns, such as tendons. Several experiments are designed specifically to test the theory that tendons and muscles are formed in the embryo by stretching between foci of concentrated traction: Surgical sponge material will be used as a substrate for the culture of dermal fibroblasts and then implanted into chicken embryos to test whether supernumerary muscles and tendons will form with the implants as their attachment sites (insertions). By removing apical ridges from early limb buds, abnormal limbs will be created lacking distal skeleton, and the peripheral attachments of their tendons will be mapped. The muscle cross-connections of mirror-imaged limbs will also be mapped. The sites on skeletal surfaces where traction is strongest will be located and compared with the normal locations of ligament and muscle connection. The mechanical effects of fibroblast traction on reprecipitated collagen will be studied by electron microscopy, to see whether the differences observed between dermis and tendons in the (65-67 nm.) collagen spacing between bands can be caused by differences in fibroblast traction. Collagen covalently labeled with ferritin will also be used to distinguish sites of secretion from sites of mechanical pulling. The motility of cells from freshwater sponges will also be studied by time lapse cinemicrography, together with their ability to rearrange vertebrate collagen into anatomical patterns characteristic of sponges. As a way of observing and measuring the ability of the cell surface to exert and resist shearing forces (and as a new approach to the problem of measuring membrane fluidity), magnetic and electric fields of controllable strength will be used to pull magnetic and charged particles across cell surfaces.